This application is a national phase of International Patent Application No. PCT/DE02/01509, filed Apr. 25, 2002, designating the United States of America, and published in German as WO 02/103166 A1, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany Patent Application No. 101 28 505.1, filed Jun. 14, 2001.
The invention relates to the fastening of moving blades to a disk of a turbomachine rotor. Especially preferred embodiments of the invention relate to fastening of moving blades to a disk of a gas turbine rotor, having moving-blade roots which, at least over most of their axial length, have a constant cross section with mirror-symmetrical toothlike or wavelike projections, having at least mainly axially running disk slots holding the moving-blade roots in a positive-locking manner in the radial direction and in the circumferential direction, and having in each case one riveted joint per moving blade for axially fixing the latter to the disk.
It is normal practice to provide turbine moving blades of gas turbines with toothed or wavelike roots, often referred to as “fir-tree roots”, and to hold these roots in axial disk slots in a positive-locking manner. The contact surfaces of root and slot absorb the radial centrifugal force and also flow- and acceleration-induced circumferential forces and bending moments. The axial forces have to be transmitted by additional elements. There are a number of possibilities for this, such as, for example, stop surfaces on one side of the blade roots, and plates, rings, wires, etc., which catch in slots on the other side of the blade roots in a positive-locking manner. Screwed fastenings are also known, screw holes and threads in the highly loaded disks being very critical from a strength point of view.
German Patent Document DE 195 16 694 A1 (corresponding U.S. Pat. No. 5,727,927) discloses fastening of the generic type which provides a riveted joint for absorbing the axial forces. There is one rivet per moving blade, and this rivet is directed axially between moving-blade root and disk-groove bottom from one end face to the opposite end face of the disk. The two rivet heads rest on seating plates which can compensate for small dimensional tolerances between blade and disk. During the disk exchange, the rivet heads can be removed, for example by drilling, without the risk of damaging the disk or the blade. The relatively inexpensive seating plates are renewed in any case, so that damage to them during the removal of the rivet is not important. It is admitted that this solution is relatively simple, inexpensive and easy to assemble and repair. One disadvantage, however, is that the disk slots in relation to the blade root have to be deeper than without a rivet or that there is room for only one rivet of relatively small cross section. A further, more serious disadvantage lies in the fact that the axial forces in the region of the seating plates are directed into the rivet heads, in the course of which the entire rivet head is under tensile stress. There may be an acute risk of fracture under tensile stress due to the notch effect at the shank/head transitions. At least plastic deformations may occur, which increasingly loosen the joint.
Against this background, an object of the present invention is to provide moving-blade fastening having a riveted joint, which fastening, with a moderate design outlay and considerable ease of assembly and repair and also a small space requirement, is markedly better in terms of strength and is therefore safer and more reliable.
This object is achieved according to especially embodiments of the invention by producing a turbomachine rotor, in particular of turbine moving blades to a disk of a gas turbine rotor, having moving-blade roots which, at least over most of their axial length, have a constant cross section with mirror-symmetrical toothlike or wavelike projections, having at least mainly axially running disk slots holding the moving-blade roots in a positive-locking manner in the radial direction and in the circumferential direction, and having in each case one riveted joint per moving blade for axially fixing the latter to the disk, characterized in that both each moving-blade root and the disk, in the region of each moving-blade root, in each case have an axial, integral extension, in that the extensions of moving blade and disk are opposite one another in pairs at a slight distance apart or in mutual contact, in that in each case a hole lying with its axis in a radial plane, i.e. in a transverse plane relative to the rotation axis of the disk, is formed approximately half in the extension of the moving-blade root and approximately half in the extension of the disk, and in that a rivet is inserted into each hole and fixed by plastic deformation.
An important aspect of certain preferred embodiments of the invention lies in the fact that each rivet is arranged in a radial plane relative to the rotation axis of the disk and thus transversely to the axial forces which occur. Therefore only the rivet shank is subjected to shearing load; the rivet heads are free of load to the greatest possible extent. Tensile forces occur, if at all, only in a magnitude which does not present a problem, since they only result from acceleration forces and centrifugal forces from the low rivet mass. Rivets having a relatively large shank diameter, i.e. large thickness, can be used, with the advantage of low surface pressure and small shearing stresses in the shank. The “hole halves” in the extensions of the moving-blade roots and of the disks enclose the rivet shanks to the greatest possible extent and provide for a favorable introduction of force.
Preferred configurations of the fastening according to the invention are described herein and in the claims.